03-10-2012, 12:23 PM
Gender expression and inflorescence structure of Pappea capensis Eckl. and Zeyh. (Sapindaceae)
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Abstract
Gender and the structure of the inflorescence and flowers of Pappea capensis (Sapindaceae) are investigated in a locality around Pretoria (22–27°S
and 25–32°E). The trees flower over a long period (December to April) and are basically monoecious, starting with male flowers followed by female
flowers towards the end of the flowering period, although some trees may be predominantly male and some predominantly female. The inflorescence is a
reduced thyrse with small flowers. Male flowers have five ephemeral petals, eight stamens and a rudimental pistil. Female flowers comprise a 3-lobed
ovary, a single style and stigma and eight staminodes.
Introduction
Pappea capensis (Sapindaceae) is a small tree or shrub,
indigenous to Africa with a wide distribution from the southern
Cape in South Africa to Ethiopia in the north. The seed of
Pappea capensis contains about 74% edible oil (Coates
Palgrave, 1977; Landsell, 1920; Venter and Venter, 2007)
that can be used for various purposes and might also be a source
for bio-diesel. No information about seed production is
available and there is still disagreement about the sexuality of
the trees as well as the structure and type of the inflorescence.
Most authors of books on indigenous trees of Southern Africa
concur that the trees are dioecious (Coates Palgrave, 1977;
Landsell, 1920; Palmer et al., 1972; Van Rooyen, 1984; Van
Wyk and Van Wyk, 1997; Van Wyk, 1984; Venter and Venter,
2007; White, 1962). However, Fivaz and Robbertse (1993) and
Davies and Verdcourt (1998) supplied evidence showing that
the trees are monoecious, first producing male flowers and later
producing female flowers, either on the same inflorescence or
on separate inflorescences.
Materials and methods
Observations over a period of 3 years were made on two
trees in a tree collection on the experimental farm of the
University of Pretoria (UP) (25°45’ S, 28°16’ E). Twenty more
trees growing in the wild in a locality 30 km north of Pretoria
were marked during December 2009 and visited at monthly
intervals. Material was also collected during field trips to other
parts of the wider study area (22–27°S and 25–32°E).
Herbarium specimens from the National Herbarium of Pretoria,
the Schweickerdt Herbarium at the University of Pretoria, and
the Compton Herbarium in Cape Town were also consulted.
Specimens collected during field trips and from the marked
trees have been deposited in the Schweickerdt Herbarium at the
University of Pretoria.
No special technique was applied to score sex expression of
trees. Trees that were observed in the male phase were each
bearing hundreds to thousands inflorescences, each bearing
male flowers only, while inflorescences on trees in the female
phase, borne only female flowers or female flowers with
remains of some dead male flowers amongst the female flowers.
Most herbarium specimens found in the different herbaria
were collected with male flowers and very few with female
flowers. The descriptions in this paper are therefore mainly
based on material collected and observations made during field
excursions and visits to the marked trees.
Richards (1990) states that “sex expression can be controlled
by environment, irrespective of size and age” and that “… less
salubrious niches tended to induce maleness, and more optimal
sites tended to induce femaleness.” The fact that 60% of the
herbarium specimens of Pappea capensis were collected in the
male phase and that more male plants than female plants were
encountered during field excursions, can be ascribed to the
longer male phase of the trees, quite apart from any possible
environmental factors. Korpelainen (1998), working on a large
variety of plant taxa, stated that stress caused by less than
optimal levels of light, nutrition, weather or water, often favour
maleness. Kang (2007), working with pine trees, found that
over a 5-year period, 37% of the trees changed their sexual
system at least once, ranging from monoecy to male.